A first pipeline, such as a main sewer pipe, is generally bonded in a liquid tight manner to a second pipeline, such as a branch pipe, at a portion connecting the two pipelines by means of a bonding agent such as mortar. In general, the bonding agent may be removed from the first or second pipelines by only slightly relatively displacing the pipelines. As a result, a space is formed in the connection portion, and the liquid tightness of the connection portion is lowered. A cut-off treatment is performed to prevent water leakage from the space formed in the connection portion.
This water cut-off is generally accomplished by a chemical feeding method involving the injection of a cut-off agent of cement or liquid type into the space and around the connection portion followed by coagulation of the cut-off agent.
When water leakage occurs in practice, the cut-off agent is diluted with water, flows into the pipeline and frequently fails to harden. Consequently, subsequent treatment for removing the cut-off agent that has entered the pipeline should also be conducted.
In the chemical feeding method using a cement-type cut-off agent, the hardened cut-off agent does not exhibit elasticity. When the pipes are displaced due to vibration, land subsidence or the like, the hardened cut-off agent peels from the pipeline, and cracks form in the hardened cut-off agent. As a result, long-term, stable water cut-off is not expected In the chemical feeding method using a liquid-type cut-off agent, the mechanical strength of the cut-off agent is low. The water cut-off is therefore not stably maintained for a long period of time.